Allow ParentWindowHandle to be Send + Sync

src/platform/macos/mod.rs

@@ -12,7 +12,7 @@ use dispatch2::MainThreadBound;
 pub use error::Error;
 use objc2::__framework_prelude::Retained;
 use objc2::rc::Weak;
-use objc2::MainThreadMarker;
+use objc2::{MainThreadMarker, MainThreadOnly};
 use objc2_app_kit::NSView;
 use raw_window_handle::{DisplayHandle, HasWindowHandle};
 use std::fmt;
@@ -69,9 +69,9 @@ impl fmt::Debug for PlatformHandle {
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug)]
 pub struct ParentWindowHandle {
-    view: Retained<NSView>,
+    view: MainThreadBound<Retained<NSView>>,
 }
 
 impl ParentWindowHandle {
@@ -80,6 +80,26 @@ impl ParentWindowHandle {
     ) -> core::result::Result<Self, ParentWindowHandleError> {
         let view = extract_raw_window_handle(window.window_handle()?)?;
 
-        Ok(Self { view })
+        let mtm = view.mtm();
+        Ok(Self { view: MainThreadBound::new(view, mtm) })
     }
 }
+
+impl Clone for ParentWindowHandle {
+    fn clone(&self) -> Self {
+        // SAFETY: We only use Retained::clone, which is thread-safe
+        let mtm = unsafe { MainThreadMarker::new_unchecked() };
+        let view = self.view.get(mtm);
+        Self { view: MainThreadBound::new(view.clone(), mtm) }
+    }
+}
+
+impl PartialEq for ParentWindowHandle {
+    fn eq(&self, other: &Self) -> bool {
+        // SAFETY: We only use Retained::eq, which is thread-safe
+        let mtm = unsafe { MainThreadMarker::new_unchecked() };
+        Retained::eq(self.view.get(mtm), other.view.get(mtm))
+    }
+}
+
+impl Eq for ParentWindowHandle {}

src/platform/macos/window.rs

@@ -39,7 +39,7 @@ impl WindowHandle {
             let _ = NSApplication::sharedApplication(mtm);
 
             if let Some(parent) = init.settings.parent.take() {
-                return Self::create_window_parented(init, parent.inner.view, mtm);
+                return Self::create_window_parented(init, parent.inner.view.into_inner(mtm), mtm);
             }
 
             Self::create_window_standalone(init, mtm)
@@ -126,7 +126,7 @@ impl WindowHandle {
         let Some(view) = self.view.load() else { return Ok(()) };
         let Some(view) = view.inner_ref() else { return Ok(()) };
 
-        BaseviewView::set_parent(view, new_parent.view);
+        BaseviewView::set_parent(view, new_parent.view.into_inner(view.mtm));
 
         Ok(())
     }

src/platform/win/mod.rs

@@ -54,6 +54,11 @@ pub struct ParentWindowHandle {
     handle: HWnd,
 }
 
+// SAFETY: ParentWindowHandle does not actually expose any thread-unsafe operation
+unsafe impl Send for ParentWindowHandle {}
+// SAFETY: ParentWindowHandle does not actually expose any thread-unsafe operation
+unsafe impl Sync for ParentWindowHandle {}
+
 impl ParentWindowHandle {
     pub fn extract(
         parent: &impl HasWindowHandle,

src/settings.rs

@@ -145,6 +145,12 @@ pub struct ParentWindowHandle {
     pub(crate) inner: platform::ParentWindowHandle,
 }
 
+// Assert this is Send+Sync
+const _: () = {
+    const fn foo<T: Send + Sync>() {}
+    foo::<ParentWindowHandle>();
+};
+
 impl ParentWindowHandle {
     /// Grabs a handle to the given `parent_window`, to later create a child window in it.
     pub fn from_window(parent_window: &impl HasWindowHandle) -> Self {